Make quote tell prefix case insensitive

bot.py

@@ -871,7 +871,7 @@ async def quote_tell_slash(ctx: SlashContext, author: str, prefix: Optional[str]
         return
     if prefix is not None:
         for quote in quotes:
-            if quote.startswith(prefix):
+            if quote.lower().startswith(prefix.lower()):
                 await _do_quote(ctx, author, quote, tts)
                 return